It is known that the formation of extruded foams in the form of billets or boards is enhanced by the employment of a vacuum chamber so that the expansion of the foam is accomplished under subatmospheric pressure. Examples of vacuum foam extrusion apparatus and methods may be seen in prior U.S. Pat. Nos. to Nelson et al 3,584,108, Maxon 3,169,272, Cogiano 3,822,331 and U.K. Pat. No. 1,233,088. In vacuum extrusion technology, a most difficult problem to solve is the curing and extraction of the material from the vacuum chamber, especially delicate or fragile material such as styrene foam in the form of large boards or billets. This problem has been solved by the employment of an inclined barometric leg as seen in applicant's prior U.S. Pat. Nos. 3,704,083 and 4,044,084.
On a small or laboratory scale, the construction and operation of a barometric leg is a relatively simple matter. However, in a large scale plant, a number of problems are encountered in the construction, fabrication and operation of the leg. For example, the size of the leg itself creates a number of problems in view of the forces thereon when the leg is evacuated to form the vacuum chamber and essentially to fill the leg with water.